Preparation method of lithium iron phosphate positive electrode material, lithium iron phosphate positive electrode material, positive plate and lithium ion battery

Abstract

The invention relates to the field of lithium battery materials, and particularly discloses a preparation method of a lithium iron phosphate positive electrode material, the lithium iron phosphate positive electrode material, a positive plate and a lithium ion battery. The composite carbon source is added in the preparation process of the lithium iron phosphate positive electrode material, so that the prepared lithium iron phosphate positive electrode material can form an excellent conductive network structure, and further, the prepared lithium ion battery has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery materials, and in particular to a method for preparing a lithium iron phosphate positive electrode material, a lithium iron phosphate positive electrode material, a positive electrode sheet and a lithium ion battery. Background Art

[0002] Lithium-ion batteries have high volumetric energy density and mass energy density and excellent cycle performance. They are recognized as an ideal energy source internationally today and are also a new generation of green high-energy batteries. They are widely used in portable devices such as mobile phones and digital cameras, large mobile energy fields such as plug-in hybrid vehicles and pure electric vehicles, and fixed energy fields such as energy storage power stations and UPS.

[0003] The cathode materials used in lithium-ion batteries are mainly ternary materials and lithium iron phosphate. Among them, lithium iron phosphate has been widely used in the field of lithium batteries due to its excellent cycle performance, structural stability, safety and low cost. However, the low working voltage and energy density of lithium iron phosphate have seriously restricted the development of lithium iron phosphate in cathode materials.

[0004] In the prior art, lithium iron phosphate materials are often modified to obtain positive electrode materials with relatively excellent electrochemical properties. For example, patent CN115775886A discloses a method for preparing lithium iron phosphate / carbon fiber composite materials. The patent uses carbon fiber materials to modify lithium iron phosphate, which solves the problem of easy agglomeration and poor density of material particles in the process of preparing battery materials, thereby making the lithium battery have excellent electrochemical properties. For another example, patent CN118851128A discloses a modified lithium iron phosphate and its preparation method, positive electrode sheet, and secondary battery. The patent uses carbon sources and nitrogen sources to make lithium iron phosphate still have excellent electrochemical properties under low temperature conditions. However, the preparation method of lithium iron phosphate in the prior art still has the problems of complex operation, expensive raw materials, inability to be promoted, and the lithium iron phosphate prepared cannot have excellent cycle performance, working voltage and energy density at the same time. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art that lithium iron phosphate cannot have both excellent cycle performance and energy density, and to provide a method for preparing lithium iron phosphate. The lithium iron phosphate positive electrode material prepared by the method can have both excellent cycle performance and energy density, and is simple to operate, cost-effective and easy to promote.

[0006] In order to achieve the above object, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, the method comprising:

[0007] S1: preparing a first slurry containing a lithium iron phosphate raw material and a first carbon source, placing the first slurry in a hydrothermal reactor for a first reaction, and then performing a first drying treatment on the first slurry to prepare a lithium iron phosphate precursor;

[0008] S2: preparing a second slurry containing a lithium iron phosphate precursor and a second carbon source, and then sequentially performing a second drying process and a calcination process on the second slurry to prepare the lithium iron phosphate material positive electrode material;

[0009] Wherein, the first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acids, salicylic acid, tartaric acid, oxalic acid and polysorbate;

[0010] The mass ratio of the first carbon source to the second carbon source is 1:1-2.

[0011] The second aspect of the present invention provides a lithium iron phosphate positive electrode material prepared by the preparation method described in the first aspect of the present invention.

[0012] A third aspect of the present invention provides a positive electrode sheet coated with the lithium iron phosphate positive electrode material described in the second aspect of the present invention.

[0013] A fourth aspect of the present invention provides a lithium battery, wherein the positive electrode sheet of the lithium battery is the positive electrode sheet described in the third aspect of the present invention.

[0014] By adopting the above technical solution, a composite carbon source is added during the preparation of the lithium iron phosphate positive electrode material, so that the prepared lithium iron phosphate positive electrode material can form an excellent conductive network structure, and further the prepared lithium ion battery has excellent electrochemical properties. DETAILED DESCRIPTION

[0015] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0016] One aspect of the present invention provides a method for preparing a lithium iron phosphate positive electrode material, the method comprising:

[0017] S1: preparing a first slurry containing a lithium iron phosphate raw material and a first carbon source, placing the first slurry in a hydrothermal reactor for a first reaction, and then performing a first drying treatment on the first slurry to prepare a lithium iron phosphate precursor;

[0018] S2: preparing a second slurry containing a lithium iron phosphate precursor and a second carbon source, and then sequentially performing a second drying process and a calcination process on the second slurry to prepare the lithium iron phosphate material positive electrode material;

[0019] Wherein, the first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acids, salicylic acid, tartaric acid, oxalic acid and polysorbate;

[0020] The mass ratio of the first carbon source to the second carbon source is 1:1-2.

[0021] In the present invention, preferably, the method for preparing the first slurry includes: placing the lithium iron phosphate raw material and the first carbon source in deionized water for a first mixing treatment. Preferably, the conditions of the first mixing treatment include: a temperature of 20-40°C and a time of 1-3 hours. More preferably, in the first mixing treatment, based on the mass of the lithium iron phosphate raw material, the amount of deionized water used is 80-120wt%, preferably 90-110wt%.

[0022] In the present invention, preferably, based on the mass of the lithium iron phosphate raw material, the addition amount of the first carbon source is 1-5wt%, preferably 1.5-4wt%, for example, it can be 1.5wt%, 2wt%, 2.5wt%, 2.7wt%, 3.0wt%, 3.2wt%, 3.5wt%, 4wt% and the like and the range between any values ​​thereof.

[0023] In the present invention, preferably, the method for preparing the second slurry comprises: placing the lithium iron phosphate precursor and the second carbon source in deionized water for a second mixing treatment. Preferably, the conditions of the second mixing treatment include: a temperature of 25-45° C. and a time of 2-4 hours. More preferably, in the second mixing treatment, based on the mass of the lithium iron phosphate raw material, the amount of deionized water used is 85-125wt%, preferably 95-110wt%.

[0024] In the present invention, by improving the coordination effect of the first carbon source and the second carbon source, the prepared lithium iron phosphate positive electrode material has excellent electrochemical properties. Preferably, the mass ratio of the first carbon source to the second carbon source is 1:1.2-1.8, for example, it can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8 and the range between any ratios thereof.

[0025] In the present invention, preferably, the lithium iron phosphate raw material includes a lithium source, an iron source and a phosphorus source.

[0026] In the present invention, in order to further improve the electrochemical performance of the lithium iron phosphate positive electrode material, preferably, the lithium source is selected from Li 2 CO 3 , LiOH and LiH 2 PO 4 Preferably, the iron source is selected from FeSO 4 、FeC 6 H 5 O 7 and FeC 2 O 4 Preferably, the phosphorus source is selected from H 3 PO 4 NH 4 ) 2 HPO 4 and (NH 4 ) 3 PO 4 At least one of .

[0027] In the present invention, by reasonably adjusting the amount of lithium iron phosphate raw materials including lithium source, iron source and phosphorus source, the electrochemical properties of the subsequent lithium iron phosphate positive electrode material can be improved. Preferably, the molar ratio of lithium, iron and phosphorus in the lithium iron phosphate raw material is 1:0.1-1:0.1-1, preferably 1:0.2-0.8:0.2-0.8, for example, it can be 1:0.2:0.2, 1:0.2:0.8, 1:0.8:0.2, 1:0.8:0.8 and the like and the range between any ratios thereof.

[0028] In the present invention, preferably, the conditions of the first reaction include: temperature of 140-250° C., time of 5-12 h. More preferably, the conditions of the first reaction include: temperature of 150-200° C., time of 8-10 h.

[0029] In the present invention, in order to allow the first carbon source to be better coated on the lithium iron phosphate raw material, preferably, the conditions of the first drying treatment include: temperature of 40-80°C, preferably 45-75°C, time of 2-5h, preferably 2.5-4.5h.

[0030] In the present invention, in order to allow the second carbon source to be better coated on the lithium iron phosphate precursor, preferably, the conditions of the second drying treatment include: temperature of 50-100°C, preferably 55-85°C, time of 3-6h, preferably 4.5-5.5h.

[0031] In the present invention, preferably, the calcination treatment conditions include: a temperature of 500-800° C., preferably 600-700° C., and a time of 1-6 h, preferably 2-3 h.

[0032] According to a preferred embodiment, the method for preparing the lithium iron phosphate positive electrode material further comprises: performing a first grinding treatment on the first slurry; the conditions of the first grinding treatment include: a rotation speed of 200-300 r / min; and a time of 6-10 h.

[0033] According to another preferred embodiment, the method for preparing the lithium iron phosphate positive electrode material further comprises: performing a second grinding treatment on the second slurry; the conditions of the second grinding treatment include: a rotation speed of 500-1000 r / min and a time of 3-8 h.

[0034] The second aspect of the present invention provides a lithium iron phosphate positive electrode material prepared by the preparation method described in the first aspect of the present invention.

[0035] According to the present invention, preferably, the compaction density of the lithium iron phosphate positive electrode material is 2.6-2.7 g / cm 3 .

[0036] A third aspect of the present invention provides a positive electrode sheet coated with the lithium iron phosphate positive electrode material described in the second aspect of the present invention.

[0037] According to the present invention, the preparation method of the positive electrode can adopt various methods commonly used in the art, for example, it can include the lithium iron phosphate positive electrode material, the positive electrode binder and the positive electrode solvent proposed in the present invention, coating and / or filling on the positive electrode collector, forming a positive electrode material layer on the surface of the positive electrode collector, drying, rolling or not rolling, and then the positive electrode can be obtained. Preferably, in the positive electrode material layer of the battery, the content of the lithium iron phosphate positive electrode material provided by the present invention is 85-95wt%.

[0038] In the present invention, the type of the positive electrode binder can be, for example, one or more of polypropylene, polyethylene, polyvinylidene fluoride, polyvinylidene fluoride, vinylidene fluoride hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene. Preferably, based on the lithium iron phosphate positive electrode material provided by the present invention, the amount of the positive electrode binder can be 0.01-5wt%.

[0039] In the present invention, the positive electrode material layer preferably further contains a positive electrode conductive agent, and the type of the positive electrode conductive agent can be, for example, one or more of conductive carbon black, carbon fiber, acetylene black, Ketjen black, and graphene. Preferably, based on the lithium iron phosphate positive electrode material provided by the present invention, the amount of the positive electrode conductive agent can be 0.01-5wt%.

[0040] A fourth aspect of the present invention provides a lithium battery, wherein the positive electrode sheet of the lithium battery is the positive electrode sheet described in the third aspect of the present invention.

[0041] According to the present invention, there are no particular restrictions on the negative electrode, separator and non-aqueous electrolyte of the battery, and various types of negative electrodes, separators and non-aqueous electrolytes used in the field of battery preparation (e.g., the field of lithium-ion battery preparation) can be used, as long as the positive electrode used in the battery contains the lithium iron phosphate positive electrode material provided by the present invention.

[0042] The preparation method of the negative electrode can adopt various methods commonly used in the art, for example, it can include mixing a negative electrode active material, a negative electrode binder and a negative electrode solvent, coating and / or filling on a negative electrode collector, forming a negative electrode material layer on the surface of the negative electrode collector, drying, calendering or not calendering, and then obtaining the negative electrode.

[0043] In the present invention, the negative electrode active material can be selected from artificial graphite and / or natural graphite. Preferably, in the negative electrode material layer of the battery, the content of the negative electrode active material is 80-100wt%.

[0044] According to the present invention, the negative electrode binder can be selected from one or more of polypropylene, polyethylene, polyvinylidene fluoride, fluorochloroethylene-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene. Preferably, based on the negative electrode active material, the amount of the negative electrode binder can be 0.01-5wt%.

[0045] According to the present invention, the negative electrode material layer preferably further contains a negative electrode conductive agent, and the negative electrode conductive agent can be one or more of conductive carbon black, carbon fiber, acetylene black, Ketjen black, graphene and carbon nanotubes. Preferably, based on the negative electrode active material, the amount of the negative electrode conductive agent can be 0.01-5wt%.

[0046] The types of current collectors in the positive electrode and the negative electrode are well known to those skilled in the art, and can be, for example, selected from any one of aluminum foil, copper foil, and punched steel strip.

[0047] The separator is disposed between the positive electrode and the negative electrode and has electrical insulation and liquid retention properties. The separator can be selected from various separators used in lithium-ion batteries, such as PP / PE separators, polyolefin microporous membranes, polyethylene felt, etc.

[0048] The non-aqueous electrolyte is a mixed solution of electrolyte lithium salt and non-aqueous solvent, and conventional non-aqueous electrolytes in the art can be used.

[0049] The preparation method of the battery is a conventional preparation method in the art. Generally speaking, the positive electrode and the negative electrode are separated by winding through a diaphragm layer to form an electrode group, and the obtained electrode group and non-aqueous electrolyte are sealed in a battery shell to obtain the battery provided by the present invention.

[0050] According to the present invention, the lithium-ion battery prepared by the above technical solution has excellent energy density and battery cycle performance. According to some preferred embodiments of the present invention, the lithium-ion battery prepared by the lithium iron phosphate positive electrode material of the present invention has an energy density of not less than 170wh / kg and a capacity retention rate of more than 85% after 300 cycles at 1C.

[0051] The present invention will be described in detail below through examples.

[0052] Example 1

[0053] The following examples are used to illustrate the preparation of lithium iron phosphate positive electrode materials.

[0054] S1: At room temperature (25°C, the same below), weigh 740 g of lithium iron phosphate raw material according to the molar ratio of lithium: iron: phosphorus = 1:0.8:0.8 2 CO 3 576g of FeC 2 O 4 and 528g of (NH 4 ) 2 HPO 4 , the lithium iron phosphate raw material and 50g of glucose were mixed in 2000g of deionized water for 2h to prepare a first slurry, and then the first slurry was ground at 200r / min for 6h and placed in a 180°C hydrothermal reactor for a first reaction for 8h, and then a first drying treatment was performed at 45°C for 3h to prepare a lithium iron phosphate precursor;

[0055] S2: The lithium iron phosphate precursor prepared in S1 and 80g of citric acid are placed in 2200g of deionized water, and then a second mixing treatment is carried out at 30°C for 3.5h to obtain a second slurry, and then the second slurry is ground at 500r / min for 5h, and then the second slurry is dried at 50°C for 5h and calcined at 600°C for 2h to prepare the lithium iron phosphate material positive electrode material A1.

[0056] Example 2

[0057] The following examples are used to illustrate the preparation of lithium iron phosphate positive electrode materials.

[0058] S1: At room temperature, weigh 740 g of lithium iron phosphate raw material according to the molar ratio of lithium: iron: phosphorus = 1:0.7:0.7 2 CO 3 504g of FeC 2 O 4 and 462 g of (NH 4 ) 2 HPO 4, the lithium iron phosphate raw material and 55g of glucose were mixed in 1800g of deionized water for 2.5h to prepare a first slurry, and then the first slurry was ground at 300r / min for 8h and placed in a 190°C hydrothermal reactor for a first reaction for 2h, and then a first drying treatment was performed at 50°C for 2.5h to prepare a lithium iron phosphate precursor;

[0059] S2: The lithium iron phosphate precursor prepared in S1 and 70g of citric acid are placed in 1900g of deionized water, and then a second mixing treatment is carried out at 35°C for 3.5h to obtain a second slurry, and then the second slurry is ground at 600r / min for 3.5h, and then the second slurry is dried at 55°C for 4.5h and calcined at 650°C for 2.5h to prepare lithium iron phosphate material positive electrode material A2.

[0060] Example 3

[0061] A lithium iron phosphate positive electrode material A3 was prepared in a similar manner to Example 1, except that an equal weight portion of polyethylene glycol was used instead of glucose.

[0062] Example 4

[0063] A lithium iron phosphate positive electrode material A4 was prepared by a method similar to that of Example 1, except that an equal weight portion of polyethylene glycol was used instead of citric acid.

[0064] Example 5

[0065] A lithium iron phosphate positive electrode material A5 was prepared in a similar manner to Example 1, except that 50 g of citric acid was used instead of 80 g of citric acid.

[0066] Example 6

[0067] A similar method to that of Example 1 was used, except that 100 g of citric acid was used instead of 80 g of citric acid to prepare lithium iron phosphate positive electrode material A6.

[0068] Comparative Example 1

[0069] A similar method to that of Example 1 is used, except that step S2 is: calcining the lithium iron phosphate precursor prepared in S1 at 200° C. for 2 h to prepare a lithium iron phosphate positive electrode material B1.

[0070] Comparative Example 2

[0071] A lithium iron phosphate positive electrode material B2 was prepared in a similar manner to Example 1, except that 25 g of citric acid was used instead of 80 g of citric acid.

[0072] Comparative Example 3

[0073] A similar method to that of Example 1 was used, except that 250 g of citric acid was used instead of 80 g of citric acid to prepare lithium iron phosphate positive electrode material B3.

[0074] Test Example 1

[0075] The lithium iron phosphate positive electrode material is prepared into a lithium ion battery according to the following steps, and the electrochemical performance of the battery is tested. The test results are shown in Table 1.

[0076] Preparation steps of lithium-ion batteries:

[0077] (1) Preparation of positive electrode sheet: 25 g of the lithium iron phosphate positive electrode material prepared in the above examples and comparative examples, 0.6 g of conductive carbon black and 0.8 g of polyvinylidene fluoride were mixed and placed in a solvent, and then ball-milled at a speed of 360 rpm for 4 h to obtain a slurry, and the slurry was coated on an aluminum foil and dried to obtain a positive electrode sheet;

[0078] (2) Preparation of negative electrode sheet: 30 g of natural graphite, 0.2 g of conductive carbon black and 0.5 g of polyvinylidene fluoride were mixed and placed in a solvent, and then ball-milled at a speed of 400 rpm for 5 h to obtain a slurry, and the slurry was coated on an aluminum foil and dried to obtain a negative electrode sheet;

[0079] (3) Assembly of lithium-ion batteries: In a glove box, the negative electrode sheet, PP / PE separator, and positive electrode sheet are assembled. During the process, lithium salt electrolyte is injected, and then the button cell is sealed using a sealing machine. The assembled button cell is used for subsequent electrochemical performance testing.

[0080] Test method:

[0081] (1) Energy density test method: Accurately weigh the mass of the prepared battery cell (unit: g); measure the actual discharge capacity of the battery cell (unit: Ah) through a 1C charge and discharge cycle; record the rated voltage of the battery cell (unit: volt, V); calculate the energy of the battery cell using the measured capacity and voltage, and then divide the energy by the mass of the battery cell to obtain the mass energy density (unit: Wh / kg).

[0082] (2) Cyclic performance test method: Use 1C rate for constant current-constant voltage charging. After 10 minutes of idling, use 1C rate for constant current discharge. Record the number of cycles in the process and compare the discharge capacity of each cycle with the discharge capacity of the first cycle.

[0083] Table 1

[0084] Example No. Energy density wh / kg 1C cycle / capacity retention rate Example 1 193 300 weeks, 92.2% Example 2 188 300 weeks, 91.4% Example 3 189 300 weeks, 91.6% Example 4 190 300 weeks, 91.8% Example 5 175 300 weeks, 89.2% Example 6 173 300 weeks, 88.4% Comparative Example 1 122 300 weeks, 70.2% Comparative Example 2 146 300 weeks, 79.4% Comparative Example 3 148 300 weeks, 78.2%

[0085] It can be seen from the results in Table 1 that, compared with Comparative Examples 1-3, the lithium ion batteries prepared by the preparation method of the present invention have excellent energy density and cycle performance, especially the lithium ion batteries prepared in Examples 1-4 have an energy density of not less than 185wh / kg, and a capacity retention rate of not less than 90% after 300 cycles.

[0086] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a lithium iron phosphate positive electrode material, characterized in that: The method includes: S1: preparing a first slurry containing a lithium iron phosphate raw material and a first carbon source, placing the first slurry in a hydrothermal reactor for a first reaction, and then performing a first drying treatment on the first slurry to prepare a lithium iron phosphate precursor; S2: preparing a second slurry containing a lithium iron phosphate precursor and a second carbon source, and then sequentially performing a second drying process and a calcination process on the second slurry to prepare the lithium iron phosphate material positive electrode material; Wherein, the first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acids, salicylic acid, tartaric acid, oxalic acid and polysorbate; The mass ratio of the first carbon source to the second carbon source is 1:1-2.

2. The preparation method according to claim 1, wherein The mass ratio of the first carbon source to the second carbon source is 1:1.2-1.

8.

3. The preparation method according to claim 1 or 2, wherein The lithium iron phosphate raw material includes a lithium source, an iron source and a phosphorus source; Preferably, the lithium source is selected from at least one of Li2CO3, LiOH and LiH2PO4; Preferably, the iron source is selected from at least one of FeSO4, FeC6H5O7 and FeC2O4; Preferably, the phosphorus source is selected from at least one of H3PO4, (NH4)2HPO4 and (NH4)3PO4. More preferably, the molar ratio of lithium, iron and phosphorus in the lithium iron phosphate raw material is 1:0.1-1:0.1-1, preferably 1:0.2-0.8:0.2-0.

8.

4. The preparation method according to any one of claims 1 to 3, wherein The conditions of the first reaction include: temperature of 140-250°C and time of 5-12h; Preferably, the conditions of the first reaction include: temperature of 150-200° C. and time of 8-10 h.

5. The preparation method according to any one of claims 1 to 4, wherein: The conditions of the first drying treatment include: a temperature of 40-80°C, preferably 45-75°C, and a time of 2-5h, preferably 2.5-4.5h; Preferably, the conditions of the second drying treatment include: a temperature of 50-100°C, preferably 55-85°C, and a time of 3-6h, preferably 4.5-5.5h; Preferably, the calcination treatment conditions include: a temperature of 500-800° C., preferably 600-700° C., and a time of 1-6 h, preferably 2-3 h.

6. The preparation method according to any one of claims 1 to 5, wherein: The method further includes: performing a first grinding treatment on the first slurry; the conditions of the first grinding treatment include: a rotation speed of 200-300 r / min; a time of 6-10 hours; And / or, the second slurry is subjected to a second grinding treatment; the conditions of the second grinding treatment include: a rotation speed of 500-1000 r / min and a time of 3-8 h.

7. A lithium iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 6.

8. The lithium iron phosphate positive electrode material according to claim 7, wherein: The compaction density of the lithium iron phosphate positive electrode material is 2.6-2.7 g / cm 3 .

9. A positive electrode sheet, characterized in that: The positive electrode sheet is coated with the lithium iron phosphate positive electrode material according to claim 7 or 8.

10. A lithium battery, characterized in that: The positive electrode sheet of the lithium battery is the positive electrode sheet as claimed in claim 9.